If you read up on Itagaki's comments on his design philosophies you'll find that his insights went much deeper than just "HARD GAME GOOD". He cared about getting an emotional response out of the player and he used different tactics to achieve that. Itagaki wasn't a fan of game designers that only got their ideas from other games. You needed other influences outside video games to make a game unique and interesting instead of derivative. The essence mechanic for example was inspired by his love of gambling.